Fuel tanks, such as those used on commercial vehicles, are subject to a number of safety requirements. One of these safety requirements is the inclusion of a thermal relief system that allows venting of pressure within the fuel tank. Rollover vent valves are typically used in vehicle fuel systems for venting fuel vapor pressure from the fuel tank to either the atmosphere or to a vapor recovery system. Rollover vent valves may also be used to prevent fuel from escaping from the tank during fuel slosh events due to normal vehicle operation. Rollover vents may also be used to prevent fuel loss to the environment during and following a rollover accident.
Most such valves employ a float that is more buoyant than the fuel such that it will rise with the fuel level toward a valve seat that is connected to the atmosphere or to a vapor recovery system. The float is usually fitted at its top with some type of sealing element, either included as an integral feature of the float or in the form of a separate sealing element manufactured of a fuel resistant elastomer. Such separate sealing elements have been used frequently in commercial practice to provide a more effective seal, making use of the pliable properties of an elastomeric seal to effectively seal against minor surface irregularities of a valve seat.
When fuel in the tank is below the level of the float, the valve orifice is free to pass vapor or incoming gasses out to the atmosphere. If the fuel level rises due to normal vehicle motion, the float momentarily rises, urging the valve element into contact with the valve seat, and thus preventing fuel spillage. In the event of a rollover that may position the fuel tank and the valve structure upside down, a structure, such as a steel ball with a weight greater than the float buoyancy force, is used to overcome the buoyancy of the float, causing the valve to close and thereby preventing fuel spillage.
Many patents, including U.S. Pat. No. 2,990,842 to Good, U.S. Pat. No. 4,770,201 to Zakai, U.S. Pat. No. 4,886,089 to Gabrlik, and U.S. Pat. No. 4,753,262 and U.S. Pat. No. 5,313,977 to Bergsma, disclose designs employing floats with elastomeric seals.